The present invention relates in general to circulators for the non-reciprocal transmission of electro-magnetic energy. More particularly, the invention pertains to improved Y-junction waveguide circulators.
The conventional three-port waveguide circulator employs three waveguide arms that are arranged at angles of 120.degree. with respect to one another and meet at a common junction. One or more gyromagnetic members may be centrally disposed at the junction on a transformer plate or step. These gyromagnetic members are for producing non-reciprocal circulation. The quarter wavelength transformer extending from the boundary of the gyromagnetic material to the step or junction is usually required to improve the performance over a given frequency band. U.S. Pat. No. 3,886,497 shows one such waveguide circulator that comprises a transformer plate symmetrically disposed at the junction and extending across each of the arms of the circulator. These prior art circulators have some operating limitations associated therewith. For example they may not have a sufficiently high performance within a conventional band. Also, these prior art circulators are limited dimensionally and cannot be constructed in smaller sizes.
Accordingly, one object of the present invention is to provide a Y-junction microwave circulator that is characterized by an improved broadband response.
Another object of the present invention is to provide an improved microwave circulator in accordance with the principles of this invention and which is characterized by an improved return loss. This improved return loss may be on the order of 4-5 db for a 10%-15% band.
A further object of the present invention is to provide a three-port microwave circulator that is generally smaller in size than prior art circulators and in particular where the length of the arms of the circulator can be reduced in size with the construction according to this invention.
Still a further object of the present invention is to provide a means for constructing a four-port circulator of reduced overall size.
Analogous coaxial devices employ Uniform TEM mode transmission line transformers and are characterized by bandwidths of up to 50% or even octave bandwidths. However, the typical waveguide circular such as shown in U.S. Pat. No. 3,886,497, has a narrower bandwidth typically between 10%-20% for 20 dB return loss when matched with a standard single step transformer. In comparing the performance of this invention with a typical circulator, for a given performance level of say 20dB return loss the bandwidth will be larger with the device of this invention. Analogously, for a given bandwidth the performance level with the device of this invention is higher by 4-5dB.
Accordingly, another object of this invention is to provide an improved waveguide circulator that displays bandwidth characteristics more nearly like a coaxial circulator by employing a transformer more nearly like a TEM mode transmission line transformer.